$ { {-2} \times \left[\begin{array}{rrr}{2} & {1} & {2} \\ {1} & {1} & {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-2}\times{2} & {-2}\times{1} & {-2}\times{2} \\ {-2}\times{1} & {-2}\times{1} & {-2}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-4} & {-2} & {-4} \\ {-2} & {-2} & {2}\end{array}\right]}$